I have used flannel alot and have alway used a 1/4 inch seam and I have never washed it first - matter of fact I am doing one now (lodge cabin) - I have never had any problem with them - after I quilt them and wash them they are so soft and everyone loves them.... I use fannel here in alaska cost 10.50 a yard or more... I work for fabric... but I have noticed that my ufo that sit for a long period of time have started to ravel --- but never had any really ravel except one a red and black check brought from joanne's fabric... good luck --